Commercial aircraft in particular have an air conditioning system with corresponding air supply devices for air conditioning the aircraft interior, in particular the passenger cabin and the cockpit. In this connection a central air supply system controlled, for example, via the cockpit serves above all to constantly supply fresh air, which is necessary on account of the high passenger density in an aircraft cabin. The fresh air is taken as so called bleed air from the aircraft power unit and routed into the interior of the aircraft through air inlet openings. This hot fresh air is cooled to approximately 0° C. and dehumidified in a further step.
A fresh air stream of 0.55 lb/min of fresh air per passenger is required to ventilate the cabin according to the main requirements within safety-relevant regulations of the FAA (Federal Aviation Administration) and JAA (Joint Aviation Authorities). However the fresh air which is tapped off the aircraft power unit is not as a rule sufficient for this, therefore a proportion of used air (i.e. air from the interior of the aircraft, which has already been partly consumed by carried passengers through their respiratory process) is added by mixing to guarantee the required air speeds. This mixed air passes via an air distributor system via so-called “riser ducts” to the passenger areas in the top deck of the aircraft.
The admixture of used air also has the advantage of already being at the desired temperature and having a certain humidity due to the respiratory process of the passengers. If the conditioned fresh air is mixed with a certain proportion of used air, the mixed air which is supplied via the air supply system is felt to be more pleasant by the passengers, as it is less dry and warmer than the fresh air which is conditioned and dehumidified in a special unit. A further advantage which results from mixing used air and fresh air is to be seen in the fact that the proportion of fresh air which is required can be reduced by the proportion of supplied used air. As is known, by sucking in fresh air from the external environment of the aircraft, the aerodynamic drag of the aircraft increases. The fuel consumption of the aircraft is consequently also increased in accordance with the fresh air which is sucked in. The fuel consumption of a commercial aircraft can therefore be appreciably reduced by adding used air to fresh air by mixing.
As is known from the prior art, in order to control the mixing ratio of used air and fresh air in the riser ducts, a baffle is inserted between a first duct element to be connected and a second duct element to be connected of the riser ducts. In this case the first duct element comprises a feed line for used air (used air line) and a feed line for fresh air (fresh air line).
A device of this kind, which is known from the prior art, for connecting two duct elements is shown in FIGS. 1 to 3, in which a first duct element 12, a second duct element 14 as well as a baffle (not represented), which is inserted to regulate the air mixing ratio, are connected. For this purpose a respective flange (V-flange) 20, 22, which has a V-shaped cross section, is glued to each of the two areas to be connected of the first duct element 12 and the second duct element 14. The connection between the V-flanges 20, 22 is established by means of an aluminium clip 24.
The used air is supplied via a used air line 16 connected to the first duct element 12. However the fresh air is supplied via a fresh air line 18 connected to the first duct element 12.
A disadvantage known from the prior art of this duct connection lies in the fact that it represents a rigid connection without any tolerance compensation. This is to be attributed to the aluminium clip 24, which establishes a tight connection by applying a contact pressure force over the entire circumference of the V-flanges 20, 22. However undesirable stresses are introduced into the components through the applied contact pressure force if there are slight dimensional variations of the V-flanges 20, 22.
A further disadvantage which results from the duct connection represented in FIGS. 1 to 3 lies in the fact that, when calibrating the air conditioning system, the aluminium clip 24 must be completely dismantled and assembled again every time the baffle is changed. This leads to an increased assembly and dismantling expenditure and therefore to higher costs.